Shock in horses is the same as it is in humans. It is the body’s own survival mechanism when it feels death is imminent. Essentially, the circulatory system shuts down, causing a sudden drop in blood circulation and blood pressure.
“There is not enough blood to fill the blood vessels, or all the blood vessels dilate at the same time,” explained Dr. Vanessa Scanlan, a large animal veterinarian with Fundy Veterinarians, located in Shubenacadie and Truro, Nova Scotia. “If you had a pool that all of a sudden had a leak, you wouldn’t have enough water to fill the pool. It’s kind of the same thing. The effect is that there’s not enough blood to pump up the vessels that need to be pumped up.”
Deprived of oxygen and nutrients, the organs begin to fail. If the shock isn’t treated, the horse will eventually lose consciousness, the heart will stop and the horse will die.
Horses suffer shock for a number of reasons including injury, colic, extreme fear, blood loss and dehydration. The two most common types of shock that occur in horses are hypovolemic shock, which is caused by a sudden, severe blood loss due to major internal or external hemorrhaging or fluid loss through dehydration (i.e. diarrhea), and septic (or toxic) shock. Secondary to an infection, it occurs when large amounts of bacteria and endotoxins (toxins inside bacteria cells that are released when the cell is destroyed) enter the blood stream. “They cause the blood vessels to constrict and that affects the body’s cells and how they use energy,” said Dr. Alison Moore, lead veterinarian of the Ontario Ministry of Agriculture and Food’s Animal Health and Welfare department. “That decreases blood flow to the organs.”
Other forms include: cardiogenic shock, which is associated with conditions that hinder the heart’s ability to pump blood; neurogenic shock, caused by damage to the nervous system due to severe trauma, pain and stress; and anaphylactic shock resulting from a severe allergic reaction. (See Anaphylactic Shock below)
Symptoms of Shock
If horse owners find their horse in a situation where there is severe blood loss, colic or trauma, they can suspect their horse is already in or may soon suffer shock. “If they notice a quiet or depressed-looking horse with pale or slightly purple mucous membranes and they are kind of shivering and cold, that’s a good initial indication that something is not right and they’re probably feeling shock,” said Dr. Moore.
Other common symptoms include profuse sweating, a rapid, weak pulse (a heart rate over 80 beats per minute can be a sign of a serious problem) and shallow, rapid breathing ‘”because they’re not getting oxygen to the brain and the rest of the body,” she explained. The horse may also appear anxious, agitated or confused. Sometimes the horse’s temperature will be a bit low, but this isn’t always the case, Dr. Moore added.
Dr. Scanlan said horses in shock usually remain standing. “If it’s really severe, they might lie down or collapse. Horses generally don’t like to lie down. Cows, as soon as they feel off, will lie down, but horses will fight it out to the very end,” said Dr. Scanlan.
If you suspect shock, call your veterinarian immediately, urged both Dr. Moore and Dr. Scanlan. Early intervention can mean the difference between life and death.
Usually there isn’t a whole lot a horse owner can do while they’re waiting for the vet to arrive, except perhaps putting a blanket on the horse (taking care to watch for overheating) and keeping him calm by encouraging him to find a comfortable position and talking soothingly to him. If the horse is mobile, bring him to a close, safe building or shelter and put a halter on. Encourage the horse to drink.
If there is an obvious wound or other injury, tend to it as per your veterinarian’s instructions. “You really have to fix the root cause [of the shock] and your vet should be the one to direct you on that, just because there are so many things that could cause shock,” said Dr. Scanlan.
Don’t just tell your vet to come out and quickly hang up the phone – ask if there’s anything you can do in the meantime, said Dr. Scanlan, who noted that, in her experience, nosebleeds in particular should not be taken lightly and always require a call to a veterinarian. “Sometimes you can have really severe blood loss from nosebleeds in horses, often caused by fungal infections in the guttural pouches. And they can go into shock from a bad nosebleed. A lot of times it’s just an innocent bump on the nose or something, but, regardless of how severe it is, I would at least call a vet to chat with them about it,” she said.
Upon arriving, a veterinarian will do a general exam, checking the colour of the mucous membranes and heart and respiratory rate. Next is to stabilize the horse and get his blood pressure and circulation back to normal.
Usually, fluids are administered intravenously, most often a hypertonic saline – a highly concentrated salt solution that draws fluids from the tissues around the body back to the blood vessels. “It’s kind of an immediate life-saving measure,” said Dr. Scanlan.
Electrolytes may also be given as well as drugs including sedatives to calm the horse, non-steroidal anti-inflammatories, corticosteroids, antibiotics and other medications that promote circulation and reduce any effects of infection.
In many cases, the goal is to stabilize the horse before referring it to an equine hospital for blood transfusions, surgery and more intensive care, if required.
Although rare, there may be long-lasting effects – for example, sections of the gut can die off, muscles might be more susceptible to tying-up and, more chronically, kidney function can be compromised.
Seeking treatment early is the best defence against shock. If you think your horse is exhibiting symptoms, even if you aren’t positive, call a veterinarian right away. It could save his life.
Anaphylactic shock is a rare, potentially life-threatening allergic reaction to an antigen (a foreign substance that stimulates the immune system). Insect stings, certain foods or medicines and vaccines can be culprits.
When the body is exposed to the antigen, histamine and other chemicals are released into the bloodstream. They cause the blood pressure to drop quickly and cause respiratory distress, diarrhea, drooling, seizures, coma and death. Other symptoms include hives, itchiness around the head, cold limbs, rapid heartbeat and weak pulse. The reaction usually occurs almost immediately, but can happen several hours later.
Anaphylactic shock is an extreme emergency. A successful outcome depends on swift treatment. Contact a veterinarian immediately if it is suspected.
Epinephrine is used to counteract the reaction and is repeated every 15 minutes as necessary. Your veterinarian might prescribe epinephrine and train you in its use for hasty treatment should your horse suffer anaphylactic shock in the future. Corticosteroids may also be given.
It is important, however, to ensure the horse is not exposed to the antigen again, if at all possible.
MUCOUS MEMBRANES OFFER CLUES TO SHOCK
The colour of a horse’s mucous membrane – eyelids, nostrils and gums – can reveal the status of blood circulation. Gums are the most accessible mucous membranes and can offer a quick
snapshot of the horse’s health.
In a healthy horse, the gums are moist and a bright pink colour, but in a horse who has shock, they will appear very different. “Sometimes they’ll look very pale or grey. In septic shock, sometimes they appear as a bright red or a brick red,” said Nova Scotia veterinarian Dr. Vanessa Scanlan. A toxic line, a purplish discolouration on the gums just underneath the teeth, is also a hallmark sign of septic shock.
Capillary refill time (CRT) is an indicator of how well blood is circulating through the horse’s body. To check CRT, press a thumb or finger against the horse’s gums for two seconds. A white mark will result. The mark should return to a healthy pink colour within one or two seconds after you have removed your finger/thumb. If it takes longer, the horse could be in shock.